Confocal imaging techniques include the illumination of objects with a "flying spot" and the detection of light which is reflected from or otherwise remitted by the currently illuminated point on the object located only in the image plane. This provides a better spatial resolution, better contrast to the image, fast image acquisition and less depth of field, than conventional optical devices. The small depth of field allows the creation of 3-D images of semi-transparent objects.
Scanning imaging techniques are employed in confocal laser scanning microscopes (CLSM), tandem scanning microscopes (TSM), scanning laser ophthalmoscopes (SLO), and other applications.
A TSM is discussed in Petran et al, "Tandem-Scanning Reflected-Light Microscope," Journal of the Optical Society of America 1968 Vol. 58, No. 5, pp 661-664. Petran et al acknowledge that reflected-light microscopy of semi-transparent material is usually unsatisfactory because of low contrast and light scattering. They describe the TSM, in which both the object plane and the image plane are scanned in tandem. In the Peteran et al system, the object is illuminated with light passing through holes in one sector or side of a rotating scanning disk, known as a Nipkow disk. The scanning disk is imaged by the objective at the object plane. Reflected-light images of these spots thereby produced are directed to the diametrically opposite side of the same disk. Light can pass from the source to the object plane, and, from the object plane to the image plane, only through optically congruent holes on diametrically opposite sides of the rotating disk.
Tandem scanning confocal arrangement, however, are "light-starved" by the limited brightness of the illumination spot. TSM systems, in addition, are hampered by stray light scattered from the moving pinhole array.
Current flying spot systems benefit from the advent of the laser. They use moving optical elements for deflecting a laser beam, so that an illumination spot is swept across the object to be scanned.
A recent version of a CLSM is described in U.S. Pat. No. 5,532,873 of Dixon. The scanning of the laser beam is provided by two mirrors, rotationally oscillating around axes which are perpendicular to each other.
A confocal scanning laser ophthalmoscope (CSLO) is disclosed in Webb et al, "Confocal Scanning Laser Ophthalmoscope," Applied Optics, Vol. 26, No. 8, Apr. 15, 1987, pp 1492-1499. The apparatus uses multiple scanning elements, including a multifaceted rotating polygonal reflector scanner, to provide scanning of both incident and reflected light at television-rate frequencies. The CSLO scans an illumination spot over the fundus of an eye, and synchronously scans a detector over the image.
Other confocal devices, are discussed in The Handbook of Biological Confocal Microscopy, 2nd edition. Pawley, ed., Plenum Press, 1995.
Conventional scanning devices of the type discussed, require a multiplicity of mechanical components moving at high speed. They are typically bulky and require significant power to drive the scanning mechanism.
A confocal scanning device without moving parts is described in U.S. Pat. No. 5,028,802 of Webb et al. FIG. 1A of the present application (which is FIG. 1C of the '802 patent) provides a summary of the Webb et al invention and is prior art. FIG. 1B of the present application, (FIG. 3 of the '802 patent) and shows the preferred embodiment of the '802 patent.
Referring to FIG. 1C of the '802 patent (FIG. 1A of the present application), the scanning arrangement employs N.times.M array 10 of microlasers 12 in a scanning mode as the illumination source. As shown in FIG. 1A of the present application (FIG. 1C of Webb) the device includes laser scan drive 16 for energizing the lasers of array 10. The microlasers are energized sequentially, so that the array is scanned in a conventional TV raster fashion. The array is imaged on the object 18 to be illuminated, thereby providing raster illumination of the object. Light 19 emitted from the object, by reflection, scatter or transmission, is then detected by detector 20 and the detection signal, carried on line 21, is displayed synchronously with the array scan, to provide a video image on a monitor or other image output device 22 driven by SYNCH signals provided by drive 16 on line 24.
Referring to FIG. 1B of the present application (FIG. 3 of Webb), a confocal scanning configuration uses a detector array having independently addressable photodiodes, that are optically congruent to microlasers. Lens L directs light from scanned source array 10 onto the object plane OB, and light reflected from the object is directed to detector 20 by beam splitter S. A lens L' is used to direct light reflected from the object onto discrete photodiodes of a detector array 20'. These photodiodes are read individually, in a pattern that is, synchronized with the scanning-illumination of the object. Thus, light scattered from non-illuminated portions of the object does not contribute to the output of the detection device, unless it impinges upon the selected portion of the detector. As a result, noise due to unwanted scattered light is significantly reduced.
U.S. Pat. No. 5,034,613 to Denk et al issued Jul. 23, 1991, for Two-Photon Laser Microscopy discloses a laser scanning microscope in which fluorescent light is detected in a manner which avoids photo-bleaching.
U.S. Pat. No. 5,071,246 to Blaha et al issued Dec. 10, 1991, for Confocal Scanning Ophthalmoscope discloses the use of light wave conductors.
U.S. Pat. No. 5,120,953 to Harris issued Jun. 9, 1992, for Scanning Confocal Microscope Including A Single Fiber For Transmitting Light To and Receiving Light From An Object discloses the use of optical fibers for transmitting light and a light separator to divert the return light to a detector.
U.S. Pat. No. 5,296,703 to Tsien issued Mar. 22, 1994, for Scanning Confocal Microscope Using Fluorescence Detection discloses use of a beam of radiation and detection of the resulting fluorescence using beam splitters and rotatable scanning mirrors and a raster scan display.
U.S. Pat. No. 5,325,386 to Jewell et al issued Jun. 28, 1994, for Vertical-Cavity Surface Emitting Laser Array Display System discloses the use of vertical cavity surface emitting lasers in an array to enhance a display.
U.S. Pat. No. 5,386,112 to Dixon issued Jan. 31, 1995, for Apparatus and Method for Transmitted-Light and Reflected-Light Imaging discloses a microscope using a series of beam splitters and mirrors and light which is reflected is separated from light which is transmitted.
U.S. Pat. No. 5,430,509 to Kobayashi issued Jul. 4, 1995, for Scanning Laser Ophthalmoscope discloses use of beam splitters and mirrors and uses at least three scanning systems.
U.S. Pat. No. 5,450,501 to Smid issued Sep. 12, 1995, for Apparatus for the Point-by-Point Scanning of an Object uses frequency selective filtration to operate a system having transmission of light through the object being viewed.
U.S. Pat. No. 5,512,749 to Iddan et al issued Apr. 30, 1996, for Infrared Microscope discloses use of a cryogenic detection device and an IR array of detectors including a scanning mirror for scanning the object.
U.S. Pat. No. 5,524,479 to Harp et al issued Jun. 11, 1996, for Detecting System for Scanning Microscopes discloses use of a cantilevered arm as the probe to examine the object to be viewed.
U.S. Pat. No. 5,563,710 to Webb issued Oct. 8, 1996, for Imaging System With Confocally Self-Detecting Laser discloses using an array of lasers and a single detector. Also, light reflected from the object effects the lasers which then forward the light to the detector.
U.S. Pat. No. 5,568,463 to Sahara et al issued Oct. 22, 1996, for Semiconductor Laser Device To detect A Divided Reflected Light Beam discloses an optical device for detecting a magneto-optical signal in which a light-emitting portion and a light receiving portion are closely disposed on a common substrate.